Cathode



Patented Sept. 24, 1935 UNITED STATES PATENT OFFICE CATHODE Application 'December 13,1930, Serial No. 502.036

7 Claims.,

My invention relates to electron tubes and more particularly tov electron emitters.

One of the principal problems of cathodes for electronic tubes is the provision of sufficient emitting surface for emitting electrons at the necessary rate for any desired current Values. Heretofore in order to provide increased emitting surface, the laments have been arranged in the form of two or more inverted Vs connected in series, the apex of each V being supported by a hook from a common glass bead. Such a construction has at times caused a leakage between the supporting means at the apex and furthermore is not a very rugged arrangement, is expensive and difcult to assemble.

Accordingly, an object of my invention is to provide a novel cathode construction which is inexpensive and rugged.

A further object of my invention is to provide Va cathode construction which provides a maxi-V mum emitting surface in a minimum space.

Still a further object of my invention is to provide a filament construction in the form of a spiral properly supported.

According to my invention, a cathode is provided with regular outwardly projecting ribs. Specifically it comprises two cathode units using one of the cathode units as a support and winding the other unit thereon in the form of a spiral. Both units, the support and spiral winding are emitters and accordingly present a maximum electron emitting surface over a minimum length of cathode. The core carries the bulk of the current.

Referring to the drawing: l

Figure l is a diagrammatic showing of my im proved cathode construction.

Figure 2 is a cross-sectional View of a portion of the filament construction.

Figure 3 is a modification of the cathode constructions.

AS shown, the cathode comprises a first sec-` tion 2 having the usual core 3 as, for example, of hard nickel and an electron emitting coating d such, for example, as a mixture of BaO or SrO. It will be understood, however, that any other well known emitter may be used, as the particular emitter does not form a part of the invention.

Similarly, the spirally wound cathode comprises a core 6 as, for example, nickel with a coating thereon of some electron emitting material such, for example, as BaO or SrO.

In a preferred form of manufacturing my cathodes, the electron emitting coatings are (Cl. Z50-27.5)

placed on the core after the `spiral winding is Wound on the straight piece of cathode so that the emitter provides a continuous emitting surface as indicated in Figure 2.

It will be noted that the cross-sectional dimensions of the spirally wound cathode and the 'cathode support therefor are substantially the same and the separation between successive turns of the spiral windings is such that substantially an area equal to the exposed sector portion of the 10 spiral winding as, for example, between I I and I2, is exposed between I2 and I3, thus providing a maximum emitting surface.

To provide an example of the dimensions used in carrying out my invention, the diameter of the cathode core may be approximately .005, and '75 turns of the coiled Wire used per inch of emitting length.

In Figure 3 I have shown a modified arrangement of my invention in which the cathode has projecting ribs which increase the emitting surface.

While I have disclosed my invention in connection with the specific embodiment and relative dimensions, it is clear-that there may be some other suitable proportions, and I do not intend to limit myself, except as defined in the following appended claims.

Although I have illustrated the specific manner of providing the raised and depressed surfaces of the cathode, it will be clear that the same resuits may be obtained by any other means such, for example, as successive rings coiled along the first cathode. However, it will be obvious that r the spiral herein proposed will give the same effect in a much simpler fashion.

It will also be evident now that a smaller length of the cathode may be mounted in the tube to provide the same emitting surface as is now provided with a considerably longer cathode, often requiring, as stated above, two or more Vs with their attendant problems of mounting and cross leakages.

, What I claim isz- 1. A cathode structure, comprising a core; a second core of substantially equal cross-sectional dimension to said first core and being spirally Wound on said first core; and an electron emitting coating uniformly covering both of said cores, the successive turns of the spiral winding being spaced from each other at a distance to provide an exposed coated sector portion of said second core substantially equal to the adjacent exposed coated portion of said iirst core.

2. A cathode structure comprising a first core; a second core of substantially equal cross-sectional dimension as said iirst core and spirally wound on said rst core; a coating of electron emitting material uniformly covering and closely adhering to the exposed surfaces of both of said cores, the successive turns of the spiral winding of said second core being spaced from each other to provide substantially equal exposed coated surfaces of both said cores.

3. A cathode structure for thermionic discharge tubes comprising a first wire, a second wire of substantially equal diameter to and spirally wound around said first wire, both of said wires being uniformly coated with electron emitting material, the spacings of the spiral windings of said second wire being such that both wires present substantially equal exposed emitting surfaces.

ll. A cathode structure for therrnionic discharge tube comprising a core provided with regular elevations of substantially equal height to the thickness of said core, said core and said elevations being uniformly coated with electron emitting material and the spacing of said elevations being such to provide substantially equal exposed emitting surfaces of said core and said elevations.

5. In a cathode structure, the combination of a cylindrical core, a helix of wire of substanthe spacing between successive windings of said 5 helix being such as to provide substantially equal emitting surfaces of said core and said helix.

6. In a cathode structure, the combination of a cylindrical core, a helix of wire of substantially equal diameter to the diameter of said core mounted upon 4said core, a coating of electron emissive substance uniformly covering the exposed surfaces of\ both said core and said helix, the spacing between successive windings of said helix being such as to provide an exposed coated sector portion of said helix substantially equal to the adjacent exposed coated portion of said core.

7. In a cathode structure, the combination of a rst metallic wire, a helix of a second wire of substantially equal diameter to said iirst wire wound around said first wire, a coating of electron emissive substance applied to and uniformly covering both of said wires whereby the resultant emitting surface comprises the combined exposed coated surfaces of both wires, the spacing between successive turns of said helix being such as to provide substantially equal emitting surface presented by each of said wires.

PAUL G. WEILLER. 

